Method and apparatus for separating ions of respectively different specific electric charges



u y 27, 1965 u. VON ZAHN 3,197,633'

METHOD AND APPARATUS FOR SEPARATING IONS OF RESPECTIVELY DIFFERENT SPECIFIC ELECTRIC CHARGES 5 Sheets-Sheet 1 Filed Dec. 4, 1962 y 7, 1965 u. VON ZAHN 3, 97,633

METHOD AND APPARATUS'FOR SEPARATING IONS 0F RESPECTIVELY DIFFERENT SPECIFIC ELECTRIC CHARGES Filed Dec. 4, 1962 R 3 Sheets-Sheet 2 July 27, 1965 u. VON ZAHN 3,197,633

METHOD AND APPARATUS FOR SEPARATING IONS 0F RESPECTIVELY DIFFERENT SPECIFIC ELECTRIC CHARGES Filed Dec. 4, 1962 3 Sheets-Sheet 3 FIG. Ii

United States Patent METHOD AND APPARATU} FOR SEPARATING IONS 0F RESPECTIVELY DIFFERENT SPECIFIC ELECTRIC CHARGES Ulf von Zahn, Minneapolis, Minn., assignor to Siemens- Schuckertwerke Aktiengesellscliaft, Berlin-Siemensstadt and Erlangen, Germany, a corporation of Germany Filed Dec. 4, 1962, Ser. No. 242,224 12 Claims. (Cl. 250-419) My invention relates to method and apparatus for separating ions of different respective electric charges by shooting them into an electric high-frequency field between electrodes so that only ions of certain specific charges or mass can pass through the field to a collector electrode whereas other ions are caught by field-producing electrodes extending along the trajectory axis, this separation principle being known from US. Patents 2,939,952 and 2,950,389.

My invention will be described with reference to the accompanying drawings in which:

FIG. 1 shows schematically in perspective an arrangement of four field electrodes with hyperbolic electrode surfaces according to Patent 2,950,389.

FIG. 2 shows in schematic perspective a simplified mass analyzer having cylindrical electrodes, also according to the two patents mentioned above.

FIG. 3 is a schematic and perspective representation of an electrode assembly according to the invention.

FIG. 4 is a sectional illustration of the analyzer apparatus corresponding to FIG. 3.

FIG. 5 is a schematic block diagram of a mass analyzer according to the invention.

FIG. 6 shows by way of example the circuit diagram of an excitation circuit for the electrode assembly of the analyzer.

FIGS. 7a and 7b are comparative diagrams.

FIGS. 8, 9 and 10 are graphs explanatory of the method and apparatus according to the invention; and

FIG. 11 shows an example of a mass-spectrogram taken with an apparatus according to FIGS. 4, 5 and 6.

According to the above-mentioned principle of separation, the ions to be separated are shot into a periodically varying electric high-frequency field whose potential is a square function of the coordinates x, y, z of the general wherein f(t) denotes any desired periodic function of time (t), and, 0:, B, 'y are positive constants which satisfy the equation x+B= but are otherwise selectable at will.

Used in practice is almost exclusively the special case 7:0, which requires that a: B. The following relates particularly to a field-electrode assembly satisfying the latter requirement. In such a field the travelling ions, under theinfiuence of the high-frequency electric field, oscillate transversely of their forward travel in such a manner that the following two kinds of motions can be distinguished:

(l) The amplitudes of successive oscillations increase exponentially with time so that these ions impinge upon and are thus separated on the field-limiting electrodes at an earlier or later moment of their travel (inside ions).

(2) The amplitudes of all oscillations do not exceed a given maximum value depending upon the particular starting conditions with which an ion commences its travel in the square-law potential field. If this maximum value of the oscillation amplitudes is within the space enclosed by the field-producing electrode assembly, the ions can pass through the entire spectrometer to reach a collector electrode or target at the end of the analyzing portion so that they can be observed by electrical measuring methods (stable ions).

Whether a travelling ion in the analyzer field is stable or instable depends upon its specific electric charge e/m, wherein e is the electric charge and'm the mass of the particle. With suitably chosen field parameters these fields can thus be employed for separating ions of respectively different masses.

Heretofore, an analyzer field of the above-mentioned type has been produced with an assembly of four electrodes having, in the ideal case, hyperbolic surfaces facing each other, such an assembly of electrodes E being shown in FIG. 1 of the accompanying drawing. For most purposes, however, such an arrangement of hyperbolic electrodes is sufficiently approximated by four cylindrical rod electrodes of circular cross section as shown at F in FIG. 2. Even then the mutual adjustment of these electrodes rods may turn out to be intricate because at the end of the field in the travel direction of the ions, denoted by an arrow Z in FIG. 2, the spacing of each rod from the field axis, as well as the mutual distances of the rods, must be equal, and the entire system of rods must not possess any twist. The function f(t) is given a desired periodicity as well as a undirectional and constant component by employing a high-frequency voltage and a super-imposed direct voltage, for example with the aid of electric circuitry as described in the above-mentioned Patent 2,950,389. Both voltages must be supplied to the electrode system in symmetrical relation to ground potential. For this purpose, the direct voltage must possess respective equal positive and negative portions relative to ground, and the high-frequency voltage must be made accurately symmetrical, the latter being preferably done by employing a push-pull network, also as known from Patent 2,950,389.

The amount of equipment and careful adjustment thus needed for successful and optimal performance of mass spectrometry according to the above-mentioned principle is considerable; and it is an object of my invention to improve and simplify the method and apparatus in these respects.

Another, more specific object of my invention is to afford the possibility of performing the desired mass-spectro-metrical investigations with a smaller number of electrodes and correspondingly reduced requirements as to observance and maintenance of accurate adjustments.

According to my invention, these objectives are achieved by employing only a single rod electrode in conjunction with a single counter surface to provide a fixed reference potential; .1

As will be shown below, the invention is based upon a novel effect for mass separation different from the one involved in the known method with the result of also imparting to an ion separator according to the invention new functional advantages over those of the known mass spectrometric devices. v p I In analogy to the field Equation 1 presented above, the ions shot into an electric field according to the invention become subjected to a field potential which varies as a function of the transverse space coordinates (x, y) and.

time (t) approximately in accordance with the equation =f1( y )+fz( wherein f (t) and E0) are any desired periodic functions of time and only the range y lxl is utilized. This requires having the normal travel axis of the ions spaced from the origin of the x-y coordinate system. The ions passing through such a field then also travel on stable or instable paths depending upon their respective specific electric charges and are thereby separated or separately indicated.

The function f (t) is generally given a sinusoidal wave shape, although rectangular, saw-tooth, or other periodic wave shapes are alsoapplicable. The function EU) is preferably given a constant value for decelerating the ions or accelerating them as they enter into the analyzer field. However, the function 130) may also be sinusoidal for speed modulation of the ions. An applicable excitation circuit for superimposing a high-frequency voltage and a unidirectional voltage according to function f (t) is given in FIG. 6.

According to more specific features of my invention, I provide an ion separating apparatus with an ion source and a collector electrode spaced from each other in an evacuable vessel and mount between them only two mutually spaced electrodes which extend along the ion flight axis in parallel relation thereto and on opposite sides thereof between the ion source and the collector, and I apply to one of these electrodes a fixed reference potential, preferably by grounding, and to the other electrode a variable high-frequency potential to produce the analyzer field for ion separation.

According to another, preferred feature of my invention, the fixed-potential electrode is formed of two conductive and electrically interconnected surface members which form an angle with each other and extend in parallel and spaced relation to the flight axis of the ions between the ion source and the collector, whereas the other electrode consists of a single rod and is located opposite the angular surface members in a position where the rod electrode bisects the angle and has a convex surface facing the axis. As in the known apparatus, I further provide between the surface members, on the one hand, and the field electrode, on the other, the electric circuit means required for applying the periodically variable electric potential for causing the differently charged ions to either pass from the source to the collector or to be caught by the field electrode depending upon whether the specific electric charge is such that the ions travel in stable or instable paths.

According to another, more specific feature of my invention, the field electrode consists of a cylindrical rod as schematically shown at 1 in FIG. 3 of the accompanying drawings.

According to another preferred feature of my invention, the two above-mentioned surface members consist of a single angular structure (2, 3) of sheet metal, Wire-mesh material, arrays of wires, or the like. The angle formed by the two surface members 2 and 3 is preferably 90 so that the respective surfaces-represent the coordinate planes y=+x and y=x of a single quadrant. However, other angles between 60 and 120 are applicable, as well as smaller and larger angular values, depending upon the desired degree, yield or accuracy of separation.

When forming the two angularly related surface members of a single sheet-metal structure, this structure may simultaneously constitute a vacuum wall portion of the vacuum vessel.

As a rule, the angular reference structure is kept at ground potential, whereas a field potential comprising a bi h-frequency voltage V cos wt and a superimposed negative direct voltage U is impressed upon the rod electrode, this being schematically indicated in FIG. 3.

Since such an electrode arrangement is not symmertical, compared with the symmetry to the four-pole axis Z in the known equipment as represented in FIG. 2, no ion trajectories are possible with the method and apparatus according to the invention that constitute oscillations about such a symmetry axis. Nevertheless, ions can pass through the periodic field produced according to the invention, because the choice of suitable field parameters affords the production of ion paths which for many oscillations fully extend beside the four-pole axis. That is, the method according to the invention separates ions that oscillate beside the four-pole axis from ions that tend to oscillate about that axis. Added to this novel effect is thc'spearation effect caused by the different increases in amplitude of ion oscillations mentioned above.

The apparatus according to the invention, illustrated by way of example in FIG. 4, comprises an evacuable vessel 4 of elongated and substantially tubular shape in which a single cylindrical rod electrode 1 according to FIG. 3 is mounted so as to be located in bisecting relation to the angle formed by an angular counter or reference structure denoted by 2 in FIG. 4. The field electrode 1, which may either be massive or tubular, is insulated from the angle structure 2 which in turn is mounted on the wall of the vessel 4 by means of holders 5. These holders may consist of metal thus placing the structure 2 on ground potential since the vessel 4 also consists of metal and is grounded.

The analyzer portion of the vessel has a lateral branch nipple 6 for connection to a vacuum pump and is pro vided with end flanges 7 and 3 for connection to respective closure portions 9 and It) on which an ion source 11 and a collector electrode 12 respectively are mounted. The beam of ions issuing from the source 11 into the analyzer field passes through the aperture of a diaphragm 12. A corresponding diaphragm 13 is mounted in front of the collector 12. A neck portion 14 of the analyzer vessel carries an insulated conductor 15in contact with the field electrode 1.

According to FIG. 5, which shows only the electrical components of the analyzing components proper, the ion source 11 is connected to a current-supply unit 21 which is preferably energized from a utility line. The ion accelerating voltage, for example 92 volts, is then connected between the ion source and the angle structure 2. The ions themselves are produced by electron collision in the source 11. For this purpose the electrons are emitted from an incandescent filament K and shot into the source 11. Lenses L serves to focus the ions into the analyzer field. The field electrode 1 is connected through its lead 15 and a capacitor 22 with a high-frequency generator 23 and also through an inductance coil 24 with a direct-voltage source 25 which may consist of a rectifier. The highfrequency generator and the direct-voltage source 25 are preferably energized from the above-mentioned powersupply line to which the unit 21 is connected. The collector electrode 12 is grounded through the input stage of an amplifier 26 whose output circuit is connected to a recording instrument 27.

An example of a circuit for applying field voltage from the high-frequency source 23 and the rectifier 25 to the field electrode 1 is more fully shown in FIG. 6.

The invention results in a simplified mechanical design of the analyzer field assembly. The single cylindrical rod electrode 1 can be held in correct position with respect to the rectangular counter electrode 2 by means of four insulators of the same height, for example. Two of such insulators are shown at 17 and 18 in FIG. 4. They may be cemented to one of the planar surfaces of the structure 2 and extend in perpendicular relation thereto, the other end of each insulator being suitably joined with, for example cemented to, the rod 1. The two other insulating holders, not visible in FIG. 4, are preferably arranged in the same manner except that they are fastened to the other planar surface of the structure 2. The number of possible adjusting errors is thus considerably reduced, compared with the known four-pole system.

A spectrometric apparatus according to the invention can be given a smaller over-all size than a four-pole apparatus of the known type. A suitable basis of comparison is a given ion current at the collector. In comparison with a four-pole spectrometer of the known type with four cylindrical rods of unit diameter, a corresponding spectrometer according to the invention with the same unit diameter of the single rod electrode has only one-half of the ion current. This is due to more unfavorable conditions with respect to the shooting of ions into the analyzer field. Since the utilizable ion current increases approximately in linear proportion to the cross-sectional surface of the analyzer field, a spectrometer according to the invention can be made rated for the same ion current as a four-pole spectrometer of the known type with rods of unit diameter, if the rod diameter of the single field electrode is increased to the value 1- /2. It follows that in this case a spectrometer according to the invention is considerably smaller than an apparatus of the known type. This is exemplified by the comparison presented by FIGS. 7a and 7b, the former showing the geometric relations of a four-pole apparatus and the latter the corresponding relations of an apparatus according to the invention. The increase in rod diameter and the eliminatoin of three rod electrodes just compensate each other with respect to their influence upon the necessary highfrequency power. The ratio of the demand for high-frequency power to the separated ion current, therefore, is substantially the same for both types of apparatus.

If desired, the invention also affords a considerable simplification of the electrical circuitry required for operating the separator. It is no longer necessary to generate two alternating voltages 180 phase-displaced from each other, but sufiices to provide for only one alternating voltage. The necessity of push-pull circuitry is also eliminated, and only one superimposed direct voltage (negative relative to ground potential) is required, this being apparent by the example of circuitry illustrated in FIG. 6. It will be understood, of course, that modified circuits are applicable if this is desirable for special purposes.

The paths of ions that reach the collector in the apparatus according to the invention are such that a quasioptical image of the entrance aperture or diaphragm gap is projected upon the output diaphragm 13. By virtue of this property, a mass separating apparatus according to the invention achieves a given resolving power with approximately one-half of the ion-travel time required by an otherwise comparable four-pole mass spectrometer. This affords a higher ion current, a higher resolving power, or a shorter structural length of the apparatus, as may be desired in a particular case, in comparison with the four-pole apparatus.

The invention will be further explained in the followmg.

The field potential in the space between the cylindrical rod and a rectangular counter electrode can be defined by the equation:

on V d n fl( )zan j) cos (mm-E 1 and is realized only for the condition In the foregoing equation, as well as in the following derivations, the meaning of the terms employed is as follows:

=potential f =potential of the rod electrode with respect to rectangula-r counter electrode f =additional potential of both electrodes with respect to ground t=time t =moment at which the ion enters into the analyzer field a,q=substitutions in Mathieus diflerential equation d,go=coordinates of a polar coordinate system (FIG. 8)

D=distance of the rod from the apex of the angle x,y,z=coordinates of a rectangular coordinate E=phase constant n,s=summation indices =variable of Mathieus diiferential equation U=direct voltage V=high-frequency amplitude w=circular frequency B=parameter of Mathieus differential equation m=ion mass e=elementary charge FIG. 8 shows a cross section of the two electrodes in diagrammatic form for the purpose of indicating some of the above-mentioned magnitudes required for the computation presented below.

FIG. 9 is a graph showing on the abscissa the parameter magnitudes q and on the ordinate the. corresponding parameter magnitudes a. depending upon the parameters a and q, is indicated by hatching.

FIG. 10 shows schematically the in the system y relative to t or z. of this beat-frequency path is the fact that the ion travel extends for a relatively long period-of time beside the t-axis or z-axis. j j a The analytic treatment of the equation for the motion of the ions in the field between the electrodes 1 and 2, 3

path of a particle becomes particularly simple if the coefiicient a is greatly preponderant to all others. This occurs, for. example; when the diameter. D of the rod is equal to 2.3 times the field diameter D (as will more fully appear from FIG. 8 described below). Thefirst approximation for the potential 5, neglecting all values of a (n 2) and E =0 can then be written as.

=f1( z-( cos a After applying rectangular (Cartesian) coordinates: a

' x='dsin 50 for (y lxl) y dcos and inserting the potential V I f (t) =(V- cos wt-l- U) the equations for the motion of the ions, using the sub stitutions SBU; 48V mw D g mm D lead to Mathieus difierential equations 7 y( +2q s 2oy=0 The solutions of these differential equations result in the ion paths in thespectrometer. .They constitute, in the x-z plane as well as in the y-z plane, complicated oscillations which are generally-so constituted that the ions impinge upon one of the two electrodes during'the first oscillation and are thus eliminated. Consequently, vin

order to have an ion path extend throughthe entire analyzer field, the following three conditions must be ineti (a) there must always be y 0 (b) there must always be y |xl (c) there should always be y D.

sin gwtzassin s-o-t {l+2a. cos s.

wherein y(z' denotes the starting value of the ion motion at the moment t I a, denotesthe fl wherein k is a measure for the distance of then, g-value development coeflicient, and 1 A stable range of the ions,

The important property '5 from the left-hand stability limit (of the hatched area shown in FIG. 9).

Independently of the phase wt of the high-frequency voltage with which the ion commences its motion in the analyzer field, the travel path is a beat-frequency oscillation on account of the terms this being schematically represented in the graph of FIG. 10. Because a is smaller than unity, the outstanding property of this heat oscillation upon which the entire method is predicated, is the fact that the ion trajectories extend for a prolonged interval of time beside the t-axis or z-axis thus satisfying the above-mentioned condition (a). The length of the beat oscillation, measured in the number of high-frequency periods, depends only upon the a, q-value of the ion and, theoretically, can be made as long as desired. However, since the spacial length depends upon the speed of the ions, it is possible to adapt the spacial length of the beat oscillation by variation of the ion speed to an optimal extent to the length of the spectrometer equipment. In order to ascertain an ion at the collector, the first node of its beat oscillation must be located behind the end of the analyzer field. Consequently all of the ions whose energy is below a given minimum value are separated on the angular reference electrode. This minimum energy is proportional to dq, this being the distance of the a, q-value from the left stability limit (FIG. 9). When the a, q-value migrates toward the right in the stability diagram, then the beat oscillations become successively shorter and with a given ion energy a point is ultimately reached in which all ions are separated upon the angular "reference electrode. Consequently, a mass separation is possible along the entire y-stability limit, the ion currents being to a great extent independent of the adjusted ratio a/ q. This constitutes a considerable advantage over the known mass filters where the constancy of this ratio has a considerable influence upon the measured intensity ratio.

The condition (b), namely (y [x|), Can be satisfied by suitable ion injection conditions y Besides, if an ion does not meet this requirement, it is automatically eliminated in the. analyzer field.

The condition determines the position of the working range in the stability diagram near the y-stability limit. The width of this range is given by the condition (a).

Tests made with a mass spectrometer according to the invention having an analyzer field of about 27 cm.

length resulted in a sensitivity of about 3-1O A./mm.

Hg. The resolving power was approximately 190, the form of the spectral peaks was well developed.

The spectrogram shown in FIG. 11 is an example of those taken with an apparatus as described above with reference to FIGS. 3 to 6. The horizontal axis of the diagram indicates mass numbers, the vertical amplitudes are indicative of the ion current flowing to the collector as represented by the deflection of the recording instrument. The spectrogram was taken for the range of masses 14 to The apparatus used had an analyzer field length of 27 cm., a field diameter of 1.5 cm. The frequency of field excitation applied for separation of mass 28 was 1.54 megacycles per second. f (t) was always=0, which means that the angle electrode was on ground potential. The total pressure of the nitrogen-containing gas supplied to the interior .of the apparatus was 103-10 mm. Hg. The measuring range for masses 14 to 18 was found to be 3-10- amperes (as represented by the full deflection of the measuring or recording instrument). The corresponding measuring range for masses 19 to 45 was l- 10 9 A.

The sensitvity (calibrated with N was 3.0- 10* A./mm. Hg. For taking the illustrated diagram an ion accelerating voltage or 92 v. was applied between ion box 11 and angle electrode 2. The electron emission from the ion source was 1.2 mA. Used was an entrance diaphragm (12 in FIG. 4) with a diaphragm aperture of 2 mm. The resolving power was approximately 190 and the dwell time of the ions in the analyzer field was 16.5 high-frequency periods.

The diagram shows that the gas contained ions predominantly of masses 18 and 28 but also noticeable quantities of mass 44. A particular value of the diagram, as well as many others taken for other gases or under other operating conditions, resides in the fact that it combines a good shape of the spectral lines or peaks with relatively high sensitivity.

Generally methods and apparatus according to the invention are of particular advantage in cases where ion separation or mass spectrographic analysis is desired in conjunction with equipment of particularly simple design and simple attendance requirements.

I claim:

1. Apparatus for separating ions of respectively differ ent specific electric charges, comprising an evacuable vessel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, axially elongated broad-surface reference electrode means extending in parallel and spaced relation to said axis between said source and said collector, an elongated field electrode insulated from said members and extending in parallel and spaced. relation to said axis opposite said surface electrode means, said field electrode having a substantially convex surface facing said axis and having a smaller transverse width than said reference electrode means, electric circuit means connected between said electrode means and said field electrode for applying to said field electrode a periodically varying field voltage and a superimposed fixed voltage, whereby the ions travel in the field space between said electrode means and said field electrode on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

2. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable ves sel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, two axially elongated electrodes extending in mutually spaced relation parallel to said axis between said source and said collector, one of said electrodes comprising a substantially planar sheet and the other of said electrodes comprising a substantially rod-like configuration, and electric circuit means providing a high-frequency voltage and a direct voltage superimposed upon each other, said circuit means being connected between said two electrodes, whereby the ions travel in the field space between said two electrodes on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

3. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable vessel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, two axially elongated conductive and electrically interconnected sur face members forming an angle with each other and extending in parallel and spaced relation to said axis between said source and said collector, an elongated field electrode insulated from said members and extending in parallel and spaced relation to said axis opposite said surface members in a position bisecting said angle, said electrode having a convex surface facing said axis, and electric circuit means connected between said members and said electrode for applying to said electrode a periodically varying field voltage and a fixed voltage, whereby the ions travel in the field space between said members and said electrode on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

4. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable vessel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, an axially elongatedconductive structure having two surfaces extending parallel to said axis between said source and said collector and forming a right angle with each other, the bight of said angle facing said axis and being spaced therefrom, an elongated cylindrical electrode insulated from said structure and extending in parallel and spaced relation opposite said surfaces in a position bisecting said angle, and electric circuit means connected between said structure and said electrode for applying to said electrode a periodically varying field voltage and superimposed fixed voltage, whereby the ions travel in the field space between said members and said electrode on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

5. In apparatus for separating ions of different electric charges according to claim 3, said two surface members forming an assembly of metal.

6. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable vessel having an analyzer portion and two apertured diaphragms bordering said portion at opposite sides thereof and defining an ion travel axis therethrough, an ion source and ion collector means mounted in said vessel beyond said respective diaphragms and in alignment with said axis, two axially elongated conductive and electrically interconnected surface members forming an angle with each other and extending in parallel and spaced relation to said axis in said analyzer portion of said vessel, an elongated cylindrical electrode insulated from said structure and extending in parallel and spaced relation opposite said surfaces in a position bisecting said angle, and electric circuit means connected between said structure and said electrode, said circuit means having fixed ground potential at said surface members and a periodically varying field voltage and a superimposed fixed voltage at said electrode, whereby the ions travel in the field space between said members and said electrode on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

7. Apparatus for separating ions of respectively different specific electric charges, comprising means for providing ions along an ion travel axis; means for providing an electric field having a potential periodically varying as a function of the space coordinates (x, y) transverse to the ion travel axis (z) and having the form wherein 130) and f (t) are periodic functions of time, said means for providing an electric field including a pair of axially elongated electrodes, one of said electrodes comprising a substantially planar sheet and the other of said electrodes comprising a substantially rod-like configuration; and means for passing the ions through said electric field, the two coordinates x and y being in a range where y !x|, whereby the ions travel through said field on stable and instable paths depending upon their charge and are thereby separated from one another.

8. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable vessel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, axially elongated broad-surface reference electrode means extending in parallel and spaced relation to said axis between said source and said collector, an elongated field electrode insulated from said members and extending in parallel and spaced relation to said axis opposite said surface electrode means, said field electrode having a substantially convex surface facing said axis and having a smaller transverse width than said reference electrode means, electric circuit means connected between the electrode means and said field electrode for providing an electric field having. a potential periodically varying as a function of the space coordinates (x, y) transverse to the ion travel axis (z) and having the form wherein f (t) and 130) are periodic functions of time,

the two coordinates x. and y being in a range where 3 2M, whereby the ions travel in the field space between said electrode means and said field electrode on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

9. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable vessel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, axially elongated broad-surface reference electrode means extending in parallel and spaced relation to said axis between said source and said collector, an elongated field electrode insulated from said members and extending in parallel and spaced relation to said axis opposite said surface electrode means, said field electrode having a substantially convex surface facing said axis and hving a smaller transverse width than said reference electrode means, electric circuit means connected between the electrode means and said field electrode for applying to said field electrode a periodically varying field voltage and a superimposed fixed voltage to create an electric field having a potential periodically varying as a function of the space coordinates (x, y) transverse to the ion travel axis (2) and having the form wherein f,( t) and f (t) are periodic functions of time, the two coordinates x and y being in a range where YZIxI, whereby the ions travel in the field space between said electrode means and said field electrode on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

10. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable vessel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, two axially elongated electrodes extending in mutually spaced relation parallel to said axis between said source and said collector, one of said electrodes comprising a substantially planar sheet and the other of said electrodes comprising a substantially rod-like configuration, and electric circuit means for providing an electric field having a potential (1; periodically varying as a function of the space coordinates (x, y) transverse to the ion travel axis (1) and havwherein f (t) and f (t) are periodic functions of time, the two coordinates x and being in a range where 3 2M, said circuit means being connected between said two electrodes, whereby the ions travel in the field space between said two electrodes on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

11. Apparatus for separating ions of respectively different specific electric charges, comprising an evacuable vessel, an ion source and a collector axially spaced from each other in said vessel and defining a normal flight axis for ions from said source to said collector, two axially elongated electrodes extending in mutually spaced relation parallel to said axis bewteen said source and said collector, one of said electrodes comprising a substantially planar sheet and the other of said electrodes comprising a substantially rod-like configuration, and electric circuit means for providing a high-frequency voltage and a direct voltage superimposed upon each other, said circuit means being connected between said two electrodes,

whereby the high-frequency voltage and direct voltage provided by said electric circuit means creates an electric field having a potential periodically varying as a function of the space coordinates (x, y) transverse to the ion travel axis (z) and having the form =f1( -y )+f2( wherein 13(1) and f (t) are periodic functions of time, the two coordinates x and y being in a range where yZIxI, whereby the ions travel in the field space between said two electrodes on stable and instable paths depending upon their charge so that only ions of given charge reach said collector.

12. An arrangement for separating ions having different specific charges, comprising an evacuated vessel, electrode means for creating an electric field in the space between them positioned in said vessel, adjacent surfaces of said electrode means having a planar-convex shape, one of said electrode means comprising a substantially planar sheet and another of said electrode means comprising a substantially rod-like configuration, means for holding said electrode means in spaced relation, means for generating a voltage having an arbitrary periodical function of time f(t), means for supplying said voltage to said electrode means and thereby creating a time-periodical field the potential of which is a general quadratic function of the rectangular coordinates x and y of the electrode arrangement satisfying the equation y |x|, means for creating charged ions in said evacuated vessel, the said ions being introduced into said field whereby, caused by the electrostatic forces of the field executed on the ions, certain ions perform oscillations of a limited amplitude, the others, oscillations of an increasing amplitude depending on their respective specific charges and therefore follow stable and instable paths, respectively, and are thereby separated.

References Cited by the Examiner UNITED STATES PATENTS 2,249,494 7/41 Ramo 32823 X 2,772,364 11/56 VVashburn 313-63 X 2,939,952 6/60 Paul et a1. 25041.9 3,075,676 1/63 Gunther 25041.9 3,105,899 10/63 Gunther et a1. 25041.9

FOREIGN PATENTS 888,913 2/62 Great Britain.

RALPH G. NELSON, Primary Examiner. 

1. APPARATUS FOR SEPARATING IONS OF RESPECTIVELY DIFFERENT SPECIFIC ELECTRIC CHARGES, COMPRISING AN EVACUABLE VESSEL, AN ION SOURCE AND A COLLECTOR AXIALLY SPACED FROM EACH OTHER IN SAID VESSEL AND DEFINING A NORMAL FLIGHT AXIS FOR IONS FROM SAID SOURCE TO SID COLLECTOR, AXIALLY ELONGATED BROAD-SURFACE REFERENCE ELECTRODE MEANS EXTENDING IN PARALLEL AND SPACED RELATION TO SAID AXIS BETWEEN SAID SOURCE AND SAID COLLECTOR, AN ELONGATED FIELD ELECTRODE INSULATED FROM SAID MEMBERS AND EXTENDING IN PARALLEL AND SPACED RELATION TO SAID AXIS OPPOSITE SAID SURFACE ELECTRODE MEANS, SAID FIELD ELECTRODE HAVING A SUBSTANTIALLY CONVEX SURFACE FACING SAID AXIS AND HAVING A SMALLER TRANSVERSE WIDTH THAN SAID REFERENCE ELECTRODE MEANS, ELECTRIC CIRCUIT MEANS CONNECTED BETWEEN SAID ELECTRODE MEANS AND SAID FIELD ELECTRODE FOR APPLYING TO SAID FIELD ELECTRODE A PERIODICALLY VARYING FIELD VOLTAGE AND A SUPERIMPOSED FIXED VOLTAGE, WHEREBY THE IONS TRAVEL IN THE FIELD SPACE BETWEEN SAID ELECTRODE MEANS NA DSAID FIELD ELECTRODE ON STABLE AND INSTABLE PATHS DEPENDING UPON THEIR CHARGE SO THAT ONLY IONS OF GIVEN CHARGE REACH SAID COLLECTOR. 